LMT MWS assembly

[DispositionMatrix]

Non-purist content warning.

I am in the process of assembling an LMT MWS hybrid between what is now marketed as a "MARS-H 7.62 (MLKMWS-MARS)" and a "MARS-H 7.62 DMR (MLKMWSK-MARS)" in that I want an 18" or 20" DI barrel but with the longer MRP-H MLOK 15.5 LM308BML4A monolithic upper. (The low-profile gas block fits under the rail.) Lower is a MARS-HS. At this point, theoretically I have everything needed to get to the range except for a barrel. I realize building from LMT parts gets me around a lot of the knowledge that normally would be required to build an AR-10. Sights are Troy Micro MR556A1-style.

The LMT components were more than expensive. Admittedly, I did cheap out on some of the back end lower components--generic A2 grip, AERO PRECISION - AR .308 M5 CARBINE BUFFER TUBE KIT*, and B5 SOPMOD stock from Brownell's in place of a currently-unavailable $300 .308 DMR BUTTSTOCK DMR308 from LMT. I went with a Geissele G2S trigger because it was available and cheaper than all the other triggers.

*I am notably less solid on the buffer tube, spring, and buffer. Based on LMT's marketing material, I might instead want the .308 EXTENSION TUBE LMP259C (out of stock everywhere) to give me an extra 3/4" of length, which allegedly would allow for a standard AR15-style H3 buffer. Otherwise, it would appear I could use the Aero Precision milspec tube I bought along with the short, LR-308-style H3 buffer that came with it. At this point I have accumulated an assortment of LR-308-style (short) and AR-10-style (dimensionally equivalent to AR-15) H and H3 buffers. To simplify things, LMT does manufacture a MWS BUFFER TUBE KIT LM308BTK that appears to come with an AR-10-style (dimensionally equivalent to AR-15) H3 buffer, which _suggests_ it uses the .308 EXTENSION TUBE LMP259C. I'm even shakier on sourcing recoil springs separately, but have assumed the Aero Precision spring included with the kit I bought has the _correct_ spring for the included buffer.

I'm open to suggestions.

[Armed Eye Doc]

Here is a good place to look for most of the information you are seeking.

https://forum.308ar.com/topic/16799-gas-tubes-barrel-gas-ports-and-buffer-weight/

[shooterrex]

This will work for a recoil system. Call them they usually can find the parts.

https://www.armalite.com/SACItem.aspx?Item=AR10REKIT01

[98Z5V]

12 hours ago, DispositionMatrix said:

Non-purist content warning.

 AERO PRECISION - AR .308 M5 CARBINE BUFFER TUBE KIT*,

This will let you down, in a .308, especially that LMT.  What Rex stated, in the post directly above mine, is the way that you need to start, with this build and function-test of this gun.

Buy a Ballistic Advantage barrel, a Criterion barrel,  or a barrel from Fulton Armory - and send it to D.Wilson to have it converted to MWS barrel specs..

Edited April 23, 2021 by 98Z5V

[DispositionMatrix]

On 4/22/2021 at 11:45 AM, Armed Eye Doc said:

Here is a good place to look for most of the information you are seeking.

https://forum.308ar.com/topic/16799-gas-tubes-barrel-gas-ports-and-buffer-weight/

Thanks. That's a lot to digest, and now I'm trying to see how that comports with the relevant pricey LMT parts I've already acquired, such as the full auto .308 BCG (LM308DA).

[DispositionMatrix]

 

On 4/22/2021 at 1:38 PM, shooterrex said:

This will work for a recoil system. Call them they usually can find the parts.

https://www.armalite.com/SACItem.aspx?Item=AR10REKIT01

I appreciate the link. By "will work" do you mean it will work, will most likely work, or will put me on the correct path to working? Also, from a technical standpoint, what specifically makes the AR10REKIT01 kit correct/superior for, say, the mass of my full auto .308 BCG (LM308DA), assuming the gassing (ultimately) is correct? Is it the length of the tube, the spring, or the buffer size and weight?

• Is the tube, +3/4" like the .308 EXTENSION TUBE LMP259C or standard length? I noticed it's advertised as 6-position and not 7, like the LMT .308 EXTENSION TUBE LMP259C
• Is the included buffer spring a unique rate/stiffer/weaker/progressive?
• Is the buffer standard AR15-length or shorter? Is it 5.4oz or some other value?

Additionally, am I to understand that the the Armalite AR-10® 6 POSITION RECEIVER EXTENSION KIT (NO STOCK) you are recommending is a better choice for this LMT .308 build than the LMT MWS BUFFER TUBE KIT LM308BTK included in LMT's premanufactured rifles?

I am not questioning your expertise but am curious about the details.

On 4/22/2021 at 10:52 PM, 98Z5V said:

This will let you down, in a .308, especially that LMT.  What Rex stated, in the post directly above mine, is the way that you need to start, with this build and function-test of this gun.

Buy a Ballistic Advantage barrel, a Criterion barrel,  or a barrel from Fulton Armory - and send it to D.Wilson to have it converted to MWS barrel specs..

I may pull the trigger on the Armalite AR-10® 6 POSITION RECEIVER EXTENSION KIT (NO STOCK) to start the >3 month wait.

Of the 3 barrel brands you mentioned, there is not much out there in rifle-length gas, which I gather is what I need, based on earlier reading, for an 18" or 20" barrel. I would also be curious as to whether low-profile gas blocks are available for them that actually would fit under the MRP-H MLOK 15.5 LM308BML4A rail.

Based on this section of my build doc, I suspect I need to somewhat match these twist rates if sourcing a Ballistic Advantage, Criterion, or Fulton Armory barrel: 

LMT	20″ 7.62 NATO	LM308B220	20" chrome-lined DI	1:10"
LMT	20″ 7.62 NATO	LM308B220S	20" stainless DI	1:11.25"
LMT	18″ 7.62 NATO	LM308B218S	18" stainless DI	1:11.25"

I really appreciate the feedback.

Edited April 28, 2021 by DispositionMatrix

[DispositionMatrix]

I read https://308ar.com/ar-10-308-ar-compatibility-reference-guide/ and https://308ar.com/ar-10-barrel-extension-ar308-barrel-extension/, but I am still unclear on which barrel extensions are common to which manufacturers and bolts. I need to match my LMT MRP-H MLOK 15.5 LM308BML4A monolithic upper and LMT .308 BCG (LM308DA).

On Criterion's site, I am still trying to decode "DPMS PATTERN 308 HYBRID BARREL." 

Also, what is ".308 hybrid" in reference to barrels?

Edited April 28, 2021 by DispositionMatrix

[jtallen83]

48 minutes ago, DispositionMatrix said:

By "will work" do you mean it will work, will most likely work, or will put me on the correct path to working?

It works, these things are a balancing act, some manufacturers move the weights around to get the system to balance. Tungsten for the heavier buffers is expensive so they downsize the gas port to work with the lighter weight, they make compromises on gas tube length that changes dwell time, there are tons of changes you can make and still have the balance but your band of reliability seems to narrow. The Armalite kit has been found to provide the most reliable function with the widest variety of variables, you just don't find people showing up here with problems from it, the opposite, you can find numerous threads here where that kit solved the problem. There are other parts you can put together that duplicate this, you'll find that info all over the board as well, but for me it is easiest to just recommend the kit.....and to call them if it shows out of stock.

I am not familiar with LMT's 308 stuff at all so looking forward to learning a little here.

[DNP]

I may be wrong, but I believe the Hybrid is in reference to the profile. I’ve seen that a few places before. 
 

I went there to check. This is a 6.5,  it you get the idea. 

Edited April 28, 2021 by DNP

[shooterrex]

It works because this is Eugene Stoners' design. Did you know his original rifle was in 308 and only made one in 223 because the government ask him to.

Call armalite if the web shows out of stock. They can usually find parts if you talk to a human.

Hybrid is the outside profile of the barrel

[DispositionMatrix]

4 hours ago, DNP said:

I may be wrong, but I believe the Hybrid is in reference to the profile. I’ve seen that a few places before. 
 

I went there to check. This is a 6.5,  it you get the idea. 

Here is what I've gathered so far:

Barrels with rifle gas length
Brand	L	Description	PN/SKU	Twist	Journal	Material		Contour	MSRP	Gas Block	Gas Tube
Ballistic Adv	18"	.308 HEAVY PROFILE RIFLE LENGTH AR 308 BARREL, MODERN SERIES	BABL308007M	1:10"	.750	4150 CrMoV	Chrome		$240.00
Ballistic Adv	20"	.308 HEAVY PROFILE RIFLE LENGTH AR 308 BARREL, MODERN SERIES	BABL308006M	1:11"	.750	4150 CrMoV	Chrome		$250.00
Criterion	18"	DPMS PATTERN 308 HYBRID BARREL, RIFLE GAS, NITRIDE	1018S-HYR-N	1:10"	.750	SS-416R	Nitride		$359.99	Badger Ordnance TDX Gas Manifold 0.750″ Stainless Steel	BCM Gas Tube
Criterion	20"	DPMS PATTERN 308 HYBRID BARREL, RIFLE GAS, NITRIDE	1020S-HYR-N	1:11"	.750	SS-416R	Nitride		$359.99
Criterion	18"	DPMS PATTERN 308 HYBRID BARREL, RIFLE GAS, CHROME	10180-HYR	1:10"	.750	4150 CrMoV	Chrome		$359.99
Criterion	20"	DPMS PATTERN 308 HYBRID BARREL, RIFLE GAS, CHROME	10200-HYR	1:11"	.750	4150 CrMoV	Chrome		$359.99
Criterion	18"	DPMS PATTERN 308 HYBRID BARREL, RIFLE GAS, STAINLESS	1018S-HYR	1:10"	.750	SS-416R	Stainless		$339.99
Criterion	20"	DPMS PATTERN 308 HYBRID BARREL, RIFLE GAS, STAINLESS	1020S-HYR	1:11"	.750	SS-416R	Stainless		$339.99
Fulton Armory	18.5"	.308 AR, Medium Weight, 1x10, Stainless, Match Quality, FA by Criterion	FA-TU-003	1:10"	.936	410	Stainless	M110	$374.95	Gas Block, Adjustable, Low Profile, .936, Clamp On, SLR Sentry
Fulton Armory	20"	Barrel, 20", .308 AR, M110, 1x10, Stainless, Match Quality, FA by Criterion	FA-TU-005-TM-SS	1:10"	.875	410	Stainless	M110	$369.95	Gas Block, Adjustable, Low Profile, .875, Clamp On, SLR Sentry
Fulton Armory	20"	.308 AR, M110, 1x10, Stainless, Threaded, Match Quality, Krieger	FA-TU-007-SS	1:10"	.875	410	Stainless	M110	$634.95	Gas Block, Adjustable, Low Profile, .875, Clamp On, SLR Sentry

Not sure about the gas blocks for the Fulton Armory barrels fitting in the MRP-H MLOK 15.5 LM308BML4A rail.

Edited April 28, 2021 by DispositionMatrix
More info

[DNP]

Gas blocks are pretty standard sizes. You just need to get one the same size as the barrel you order. .936, .75 etc. 

[DispositionMatrix]

8 minutes ago, DNP said:

Gas blocks are pretty standard sizes. You just need to get one the same size as the barrel you order. .936, .75 etc. 

I was referring to the outer dimensions of the gas block and the unit physically fitting within the rail, which is 15.5" long. I already have matched the gas block inner diameters to the barrels in the table above. 

[shooterrex]

Gas blocks are usually smaller than the piston set up LMT usually uses. The piston set up on my CMMG is larger than a regular gas block.

[DNP]

1 hour ago, DispositionMatrix said:

I was referring to the outer dimensions of the gas block and the unit physically fitting within the rail, which is 15.5" long. I already have matched the gas block inner diameters to the barrels in the table above. 

I see that. I was trying to figure out how your chart of info under the quote of my hybrid profile post related to gas blocks. I’m easily confused. Especially by charts and numbers. 

[Matt.Cross]

11 minutes ago, DNP said:

I’m easily confused. Especially by charts and numbers. 

^^^ Dirk is the Chief Controller for the reactor at his local nuclear power plant.

[DNP]

Oh shoot...I am??

[shooterrex]

This should fit inside any rail.

https://www.cdnnsports.com/ar15-gas-block-750-low-profile-steel.html

[DispositionMatrix]

35 minutes ago, shooterrex said:

This should fit inside any rail.

https://www.cdnnsports.com/ar15-gas-block-750-low-profile-steel.html

That would seem to be the case.

 

On 4/22/2021 at 10:52 PM, 98Z5V said:

Buy a Ballistic Advantage barrel, a Criterion barrel,  or a barrel from Fulton Armory - and send it to D.Wilson to have it converted to MWS barrel specs..

I have it on good authority D. Wilson does not convert barrels for fitment with the LMT MWS (.308) upper. They do conversions for the MRP upper.

[DNP]

4 hours ago, Matt.Cross said:

^^^ Dirk is the Chief Controller for the reactor at his local nuclear power plant.

Doh!

[Matt.Cross]

6 minutes ago, DNP said:

Doh!

LOL... There's an increasingly dated reference! 

[98Z5V]

3 hours ago, DispositionMatrix said:

I have it on good authority D. Wilson does not convert barrels for fitment with the LMT MWS (.308) upper. They do conversions for the MRP upper.

Did you contact him?  Read this:

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwiu1u3CvaLwAhX_CjQIHUMEC0IQFjAAegQIAxAD&url=https%3A%2F%2Fwww.snipershide.com%2Fshooting%2Fthreads%2Flmt-mws-barrel-conversion-sleeve.6988545%2F&usg=AOvVaw02WOPDq0aZTStSxtcsF6yW

Edited April 29, 2021 by 98Z5V

[DispositionMatrix]

11 hours ago, 98Z5V said:

Did you contact him?  Read this:

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwiu1u3CvaLwAhX_CjQIHUMEC0IQFjAAegQIAxAD&url=https%3A%2F%2Fwww.snipershide.com%2Fshooting%2Fthreads%2Flmt-mws-barrel-conversion-sleeve.6988545%2F&usg=AOvVaw02WOPDq0aZTStSxtcsF6yW

Yes, I did. D. Wilson will not do a conversion for the MRP-H MLOK 15.5 LM308BML4A monolithic upper, which is just the long version of the MRP-H MLOK 12.5 UPPER LM308BML1 upper that is used on what LMT used to call their .308 "MWS" series of rifles--now called the "MARS-H 7.62" series. The MRP-H QUAD 12.75 UPPER LM308B1 upper used on the L129A1 REFERENCE RIFLE LM308SSR has the same quick-change barrel mount.

I did post in that other forum about it yesterday.

Edited April 29, 2021 by DispositionMatrix

[DispositionMatrix]

On 4/22/2021 at 1:38 PM, shooterrex said:

This will work for a recoil system. Call them they usually can find the parts.

https://www.armalite.com/SACItem.aspx?Item=AR10REKIT01

I have one of those AR10REKIT01 kits inbound from Armalite. Thanks for the link. 

Since D. Wilson has made it clear they don't do the 7.62/.308 conversion I need, I have contacted Nefarious Arms on the advice of someone in this other thread.

On the subject of barrels and gasing in particular, am I likely to have better luck getting to a modicum of reliability with 18" or with 20", assuming rifle-length gas for each? Again, this is for use with the LMT FULL-AUTO .308 BCG LM308DA I already have on hand.

[98Z5V]

2 hours ago, DispositionMatrix said:

I have one of those AR10REKIT01 kits inbound from Armalite. Thanks for the link. 

Since D. Wilson has made it clear they don't do the 7.62/.308 conversion I need, I have contacted Nefarious Arms on the advice of someone in this other thread.

On the subject of barrels and gasing in particular, am I likely to have better luck getting to a modicum of reliability with 18" or with 20", assuming rifle-length gas for each? Again, this is for use with the LMT FULL-AUTO .308 BCG LM308DA I already have on hand.

Either barrel length would work very well with a rifle gas system.